All terrain vehicles (ATV's) are a particular genre of utility/recreational vehicle that have become quite popular in recent years. Like a snowmobile, motorcycle or personal watercraft, the ATV is relatively narrow in construction, typically having a single seat straddled by a single rider. Unlike any of these other recreational vehicles, however, the ATV has four wheels. This difference introduces some interesting engineering challenges. Like a two-wheeled motorcycle, the frame needs to be relatively narrow, since it is intended to be straddled by the rider. Unlike a motorcycle, however, the ATV has four (and sometimes six) wheels--i.e., a pair of front wheels and at least a pair of rear wheels, each member of a pair being spaced laterally from one another so that the resultant vehicle is up to four feet wide. Because the ATV is designed for off-road conditions, which can be rugged at times, the frame of the vehicle must be strong enough to withstand significant torsional stresses resulting when one of the wheels encountering uneven terrain. Such torsional stresses are generally not felt by motorcycles, since they only have one front and one rear wheel. Moreover, most other types of four-wheeled vehicles (such as golf carts, cars, etc.) can be built with fairly wide frames more easily able to handle these torsional stresses, because there is no requirement that the frames of such vehicles be sufficiently narrow to permit the rider to straddle the frame.
Typically the frame of an ATV is made from a structural metal and the various vehicle systems and components are mounted to it, including an engine, a transmission, axles and associated hubs and wheels, suspensions for the wheels, a seat, steering and electrical and mechanical control mechanisms, etc. The vehicle's structural metal frame typically is constructed from several lengths of metal tubing (square, rectangular or round), each piece of which has been bent to a particular shape and cut to a precise length so that, when assembled, the frame provides a unitary skeletal structure to which the various vehicle systems and components may be mounted.
To provide points of attachment on the frame for mounting the various vehicle systems and components, brackets usually are welded to the tubular frame, the brackets having mounting holes in locations corresponding to the desired mounting positions for the various components. Due to the need for structural integrity and proper mounting of the various vehicle components to be mounted on the frame, it is not unusual for the complete frame skeleton to have over 100 parts. That is, fabrication of the frame itself (excluding all of the vehicle systems and components mounted to the frame) can require the assembly of well over 100 separate tubes and brackets.
Proper spatial alignment of many of the vehicle components must be attained to assure that the completed vehicle has the proper fit and finish. Also, certain of the vehicle components must be accurately spaced with respect to one another to provide proper alignment and operation of those components. To achieve this proper spacing and alignment, the scores of tubes and brackets must be assembled with great precision. For example, the relative mounting positions of the engine and the transmission are important for proper drive train performance. Similarly, proper geometry must be attained between the transmission and the suspension of the drive wheels. To provide the proper spatial relationships for all these mounting points, each frame for each vehicle must be constructed with a high level of accuracy and consistency--the structural tubes must consistently be cut to the proper length, bent to the proper shape, and welded together in the proper spatial configuration. The dozens of brackets secured to the structural tubes must be consistently welded to precisely the proper location and at the proper orientation to ensure that the components mounted to these brackets will have the proper spacing and orientation. Most of the welding and other assembly of the frame and brackets are done manually, making the construction and quality control of the entire frame labor intensive.